How many 5 digit number greater than 24000 can be formed if repetition of digit is allow.

Answer 1

three digits can be 0 to 9 or ten things taken 3 at a time

one digit can be 4 to 0 or seven things
one at a time

the fifth, on the left, can be 2 - 9 or 8 things

permutations of 10 things taken 3 at a time = 10!/(10!-3!) = 10*9*8
then 7!/6! = 7
then 8!/7! = 8
so
10*9*8*7*8 - 1 because 24000 itself is excluded.